Method for stabilizing bioactivity of growth factor

ABSTRACT

This invention discloses a method for stabilizing bioactivity of a growth factor, including mixing collagen with a growth factor and freeze drying the mixture to remove water. After this treatment, the bioactivity of the growth factor at room temperature remains stable for at least 7 days.

TECHNICAL FIELD

This invention discloses a method for stabilizing bioactivity of a growth factor, and a composition with bioactivity of growth factor preserved and prepared by the method.

BACKGROUND

Growth factors comprise a group of proteins responsible for signal transduction inside or between cells, and regulation of cell growth, differentiation, and other functions by binding to specific cell surface receptors.

There are many types of growth factors, including platelet-derived growth factor (PDGF), epidermal growth factor (EGF), keratinocyte growth factor (KGF), transforming growth factor (TGF-α, TGF-β), fibroblast growth factor (FGF), stem cell factor (SCF), insulin-like growth factors (IGF-I, IGF-II), nerve growth factor (NGF), bone morphogenetic protein (BMP), connective tissue growth factor (CTGF), vascular endothelial growth factor (VEGF), colony stimulating factor (CSF, M-CSF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, erythropoietin (EPO), endothelial cell monocytes active polypeptide (endothelial-monocyte activating polypeptide), epithelial neutrophil activating peptide, glial derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor (GMCSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), interleukin (IL-1, IL-2, IL-3, etc.), serotonin, tumor necrosis factor (TNF), and von Willebrand factor. Each growth factor has its corresponding receptor(s) and is therefore highly specific.

The clinical application of growth factors is very extensive, including promoting wound healing, assisting joint repair, regulating periodontal tissue regeneration, facilitating all kinds of tissue regeneration, combining with cell therapies in regenerative medicine, etc. So as related research has also made continuous progress, even for cancer treatment. Due to easy loss of bioactivity of various growth factors, especially the stability and storage of growth factors without freezing and even at room temperature are important for commercial products. Scientists usually designed various kinds of growth factors mutants through recombinant gene engineering techniques or sequence tags [Int. J. Mol. Sci. 2012, 13, 6053-60721 to prolong the bioactivity of growth factors artificially. Nevertheless, adverse effects such as cancer development may affect the normal condition of a human body. Among them, Regranex® Gel is a gel containing recombinant human platelet derived growth factor (rhPDGF). It was approved by US FDA in 1997 for the treatment of foot ulcer wounds complicated by chronic diabetes.

The rhPDGF in Regranex® Gel is genetically engineered by mutating, deleting, or replacing a naturally occurring PDGF sequence, and then placed in plasmids to produce a recombinant protein, so its bioactivity can be stabilized at room temperature. Although Regranex® Gel is very expensive, inconvenient to use, requiring low-temperature storage, its annual output value is as high as US S270 million, showing that its market demand is quite huge. However, the FDA officially announced that Regranex® Gel may increase the risk of cancer and the risk of death by up to 5 times after more than 10 years of follow-up study. This demonstrates that growth factors containing non-naturally occurring sequences, especially having prolong life-selves may be risk and may not be suitable for clinical treatment.

However, native growth factors have short half-lives and their bioactivities are rapidly degraded at room temperature, thus limiting the application of native growth factors in clinical treatment.

Munisso et al. [https://doi.org/10.1155/2019/4016351] also proposed using collagen/gelatin sponges (CGSs) to provide both protection and release of bFGF. Nevertheless, they found that the bioactivity of bFGF in CGSs, not in a dry form, can only be protected for no more than 5 days. In other words, a bioactivity drop of bFGF was significant after 7 days.

Therefore, a natural method to preserve the bioactivity of growth factors has great demands for the commercial and clinical applications. The current application proposes a natural way of drying the mixture of collagen and growth factors, and the bioactivity of growth factors can be preserved at room temperature for at least 7 days. Furthermore, the bioactivity of growth factors can be preserved with collagen containing extracellular mixtures under a dry state at room temperature. And the bioactivity of growth factors can be resumed in a wet condition.

SUMMARY

In order to solve the above problems, the present invention discloses a method for stabilizing a bioactivity of a growth factor, including: providing a native growth factor; adding a matrix molecule (e.g., a collagen, a collagen derivative, a gelatin, a hyaluronan, or a combination thereof) to the native growth factor; and performing a drying step to obtain a composition with the bioactivity of growth factor preserved. The bioactivity of the growth factor in the composition at room temperature remains stable for at least 7 days.

After the composition is at room temperature for 7 days or more (e.g., 7 to 20 days, 1-6 months, or 12 months or more), 70%±30% (e.g., 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100%) of the bioactivity, as compared to the bioactivity at day 0, can be preserved.

The term “native growth factor” refers to a growth factor that naturally exists in animal, especially in human, and its amino acid sequence has not been changed by mutations such as insertions, deletions, or replacements. Preferably, the native growth factor is one that exhibits its native activities, e.g., binding to its receptor and mediating downstream events. The native growth factor is selected from, but not limited to: platelet-derived growth factor (PDGF), epidermal growth factor (EGF), keratinocyte growth factor (KGF), transforming growth factor (TGF-α, TGF-β), fibroblast growth factor (FGF), stem cell factor (SCF), insulin-like growth factors (IGF-I, IGF-II), nerve growth factor (NGF), bone morphogenetic protein (BMP), connective tissue growth factor (CTGF), vascular endothelial growth factor (VEGF), colony-stimulating factor (CSF, M-CSF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, erythropoietin (EPO), endothelial cell monocytes active polypeptide (endothelial-monocyte activating polypeptide), epithelial neutrophil activating peptide, glial derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor (GMCSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), interleukins (IL-1, IL-2, IL-3, etc.), serotonin, tumor necrosis factor (TNF), and von Willebrand factor.

In one embodiment of the present invention, the drying step is performed by a freeze-drying or lyophilization method.

In one embodiment of the present invention, the concentration of the matrix molecule is 1 to 100 mg/ml (e.g., 3 to 60 mg/ml, 3 mg/ml, 9, mg/ml, 10 mg/ml, 20 mg/ml, 30 mg/ml, 40 mg/ml, 50 mg/ml, 60 mg/ml, 70 mg/ml, 80 mg/ml, 90 mg/ml, or 100 mg/ml), and the concentration of the growth factor is 1 ng/ml to 1 μg/ml (e.g., 10 to 900 ng/ml, 30 to 900 ng/ml, 100 to 500 ng/ml, 30 ng/ml, 60 ng/ml, 90 ng/ml, 120 ng/ml, 150 ng/ml, 180 ng/ml, 360 ng/ml, or 900 ng/ml). The concentration ratio of the native growth factor to the matrix molecule can be 1×10⁻⁹ to 1:1 (e.g., 1×10⁻³ to 1×10⁻⁶:1, or 1.67×10⁻⁸ to 3.33×10⁻⁴:1).

In one embodiment of the present invention, the composition of growth factor may be further stored between −80° C. to 37° C.

The present invention further discloses a growth factor composition in which the bioactivity of the growth factor composition can be preserved for at least seven days at room temperature. The composition is prepared by the preparation method provided by the present invention. The composition includes: a growth factor; and a matrix material. In a preferred embodiment, the concentration ratio of the growth factor to the matrix material is 1×10⁻³ to 1×10⁻⁶:1.

In one embodiment, the matrix molecule is collagen. In a preferred embodiment, the concentration of the collagen is 3-60 mg/ml.

In one embodiment of the present invention, the growth factor is selected from the group consisting of, but not limited to: platelet-derived growth factor (PDGF), epidermal growth factor (EGF), keratinocyte growth factor (KGF), transforming growth factor (TGF-α, TGF-β), fibroblast growth factor (FGF), stem cell factor (SCF), insulin-like growth factors (IGF-I, IGF-II), nerve growth factor (NGF), bone morphogenetic protein (BMP), connective tissue growth factor (CTGF), vascular endothelial growth factor (VEGF), colony stimulating factor (CSF, M-CSF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, erythropoietin (EPO), endothelial cell monocytes active polypeptide (endothelial-monocyte activating polypeptide), epithelial neutrophil activating peptide, glial derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor (GMCSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), interleukin (IL-1, IL-2, IL-3, etc.), serotonin, tumor necrosis factor (TNF), and von Willebrand factor.

In one embodiment of the present invention, the growth factor composition can be further stored at −80° C.˜37° C.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the bioactivity measurement results of a growth factor PDGF solution at day 0 and stored at −80° C. for 7 months (n=3).

FIG. 2 shows the bioactivity measurement results of a growth factor PDGF solution subjected to various cycles of freeze-thawing (n=3).

FIG. 3 shows the bioactivity measurement results of storing a growth factor PDGF solution at various time points at room temperature.

FIG. 4 shows the bioactivity measurement results of a growth factor PDGF at the indicated concentrations combined with 9 mg/mL of collagen without lyophilization in comparison with a fresh PDGF solution at 6 hours.

FIG. 5 shows the bioactivity measurement results of a growth factor PDGF at indicated various concentrations combined with 3 mg/mL of collagen and lyophilized in comparison to the bioactivity of the corresponding PDGF solution measured at 6 hours in room temperature.

FIG. 6 shows the bioactivity measurement results of growth factor PDGF obtained by different preparation methods. Three concentrations of PDGF were lyophilized with collagen or alone without collagen, and together with respective aqueous PDGF solutions, were stored at room temperature for 0, 1, 2, 3, 7 days prior to bioactivity assay.

FIG. 7 shows the bioactivity measurement results of various growth factors as indicated. The amounts of growth factors and collagen and their preservation condition prior to experiments are as indicated.

FIG. 8 shows the bioactivity measurement results of various growth factors as indicated. The amounts of growth factors and collagen and their preservation condition prior to experiments are as indicated.

DETAILED DESCRIPTION

It was unexpectedly discovered that the bioactivity of a native growth factor can be stabilized at room temperature by mixing the growth factor with a matrix molecule and subjecting the mixture to a drying or lyophilization process.

A matrix molecule can be an extracellular molecule found in the extracellular matrix. Examples are, but are not limited to, collagen, hyaluronan, gelatin, fibronectin, elastin, tenacin, laminin, vitronectin, aggrecan, polypeptides, heparan sulfate, chondroitin, chondroitin sulfate, keratan, keratan sulfate, dermatan sulfate, carrageenan, heparin, chitin, chitosan, alginate, agarose, agar, cellulose, methyl cellulose, carboxyl methyl cellulose, glycogen and derivatives thereof. In addition, the matrix molecule can be fibrin, fibrinogen, thrombin, and polyglutamic acid, a synthetic polymer (e.g., acrylate, polylactic acid, polyglycolic acid, or poly(lactic-co-glycolic acid), silk fibroin, polylysine, polyamino acids.

Any of the naturally-occurring collagens or their functional variants can be used. At the present time, at least 28 genetically distinct species of collagens have been discovered. Collagen can be easily isolated and purified from collagen-rich tissues such as skin, tendon, ligament, and bone of humans and animals. Methods for isolating and purifying collagen are well known in the art. (See, e.g., U.S. Pat. No. 5,512,291; US Patent Publication 20040138695; Methods in Enzymology, vol. 82, pp. 33-64, 1982; The Preparation of Highly Purified Insoluble Collagen, Oneson, I., et al., Am. Leather Chemists Assoc., Vol. LXV, pp. 440-450, 1970; U.S. Pat. No. 6,090,996). Collagen can also be prepared by recombinant technology, such as those described by Advanced Tissue Sciences (La Jolla, Calif.) or purchased from various venders (e.g., Fibrogen; South San Francisco, Calif.).

An aqueous solution containing the growth factor and the matrix molecules, and one or more other optional materials can be prepared in a buffered solution having a pH of 2-10 (e.g., a pH of 5 to 8). Low ion solutions such as saline containing 0.135 M NaCl can be used.

The solution is subjected to a drying process to remove water from the solution. Any suitable drying process known in the art can be used, e.g., freeze-drying, lyophilization, and vacuum drying.

Once the bioactivity of a growth factor is preserved by combining with a matrix molecule, the addition of other components can still maintain the bioactivity of the growth factor. Preserving the composition in a dry state is also key to maintaining the bioactivity of the growth factor.

EXAMPLES Example 1: Construction of Recombinant Human PDGF B (rhPDGF B) Expression Vectors and Purification of rhPDGF B

The linear DNA fragments encoding native hPDGF B was obtained from pCMV-SPORT6 (Invitrogen, Grand Island, N.Y. USA) by PCR performed with a sense primer (5′-GGA TTC AGC CTG GGT TCC CTG ACC ATT-3′; SEQ ID NO: 1) and anti-sense primers (5′-GCA GCT GCA CGG CCT GTG ACC TGA-3′; SEQ ID NO: 2) in which the EcoR I sites were introduced. The resulting rhPDGF B cDNA fragment was double digested with EcoR I (TaKaRa, Japan), purified by agarose gel electrophoresis, and cloned into pPICZαA to yield pPICZαA/rhPDGF B. The procedures for small scale preparation of plasmid, digestion with restriction enzymes, ligation, and transformation all followed the standard methods. PCR was carried out using 2.5 U of Taq DNA polymerase (TaKaRa) in a final volume of 50 μL using the following conditions: 95° C. for 10 min, 30 cycles (95° C. for 60 s, 55° C. for 30 s, and 72° C. for 60 s) and a final extension at 72° C. for 7 min.

Electroporation of X33 and Screening for Recombinant Strains

The plasmids pPICZαA/rhPDGF B was linearized with Sac I and transformed into yeast Pichia pastoris strain X33 using the electroporation method according to the supplier's instruction. Transformed cells were then plated onto YPDS containing 100 μg/mL zeocin and incubated at 30° C. for at least 3 days. Single colonies were transferred simultaneously onto Minimal Methanol Medium (MM) and Minimal Dextrose Medium (MD) plates to test their methanol utilization phenotype. The MM and MD plates were incubated at 30° C. for 2 days to distinguish between the Mut^(s) and Mut⁺ recombinants. Recombinant strains containing the rhPDGF B gene were screened by colony PCR. Several clones with the Mut⁺ phenotype that expressed the maximal levels of rhPDGF B was chosen in small-scale expression and stored in YPD containing 15% glycerol for further scale-up cultures.

Overexpression of rhPDGF B in Yeast

Selected colonies of zeocin-resistant transformants were inoculated into 5 mL of Yeast Extract-Pepttone-Dextrose (YPD) broth (1% yeast extract, 2% peptone, 2% glucose) containing 100 μg/mL zeocin at 30° C., grown to stationary phase, and used to inoculate 300 mL of Buffered Glycerol-complex Medium (BMGY). After incubation at 30° C. with shaking at 100 rpm, the cells were centrifuged at 3,000×g for 10 min and the pellets resuspended in 1000 mL of Buffered Methanol-Complex Medium (BMMY) to OD₆₀₀ of 1. The cells were allowed to grow for 72 h at 30° C., and methanol was added every 24 h to a final concentration of 0.5˜1% (v/v) to induce expression of the target protein. After 72 h, cells were removed by centrifugation at 3,000×g for 5 min, and the supernatants were collected. For recombinant protein detection, the supernatants were analyzed by 15% (w/v) SDS-PAGE.

Secretion of the mature protein was expected to result in protein glycosylation. The construct contained the yeast α-factor promoter, which directs the secretion of rhPDGF B, followed immediately by the sequence for mature rhPDGF B beginning with the glutamate at amino acid position 1.

Purification of rhPDGF B from Yeast

Culture supernatants were applied to a phenyl column (GE Healthcare, Piscataway, N.J. USA) pre-equilibrated with buffer (0.01 M sodium phosphate, 1.5 M ammonium sulfate; pH 6). After loading, the column was washed with the same buffer and eluted with a linear gradient of 1.5˜0 M ammonium sulfate in the same buffer. The active fractions (5 mL) were collected using a flow rate of 60 mL/h. After centrifugation at 20,000×g for 30 min at 4° C., each sample was loaded onto a CM-Sepharose (GE Healthcare, Piscataway, N.J. USA) column pre-equilibrated with 0.01 M sodium phosphate buffer, pH 6 using an AKTA explorer 10S system. Fractions containing rhPDGF B were eluted with the same buffer containing 1 M NaCl and collected at a flow rate of 120 mL/h. The eluted solution containing rhPDGF B was concentrated using filter devices with centrifugation at 3,000×g for 60 min at 4° C. and analyzed by 15% SDS-PAGE using Coomassie brilliant blue staining. Western blotting with goat anti-His antibody (1:1000) (Clontech, Mountain View, Calif. USA) was used to detect rhPDGF B with 6-His tag overexpressed from culture supernatant derived from Pichia transformants carry rhPDGF B-6His tag. The amount of purified rhPDGF B was determined by BCA protein analysis using bovine serum albumin (BSA) as a standard.

Example 2: PDGF Bioactivity Detected by Luciferase Reporter Cells with Overexpression of PDGFRβ

The 293-SL/PR cell line was a transformed cell line expressing a PDGF receptor PDGFRβ on the surface of a 293T cell line. The 293-SL/PR cells were seeded at 1×10⁴ cells/cm² in cultural wells. After cell attachment in DMEM-10% FBS for 20 hours, serum starvation was performed for 16 hours, then different concentrations of PDGF in DMEM-2% FBS were added and cultured at 37° C. in an incubator with 5% CO₂. At various time points, cells were lysed with 1× Cell Culture Lysis Buffer (Promega) at room temperature with shaking for 15 min, then were centrifuged at 13,680×g for 10 min at 4° C. Luciferase analysis reagent (100 μL; Promega) was added to 20 μL of the supernatant and bioluminescence was measured in a luminometer (Berthold).

Example 3: Bioactivity Test at Low Temperature

Referring to FIG. 1, the bioactivity of the growth factor PDGF prepared as described above was measured by luciferase assay (day 0), and then stored at −80° C. for seven months. After that, its bioactivity was measured again. The results showed that there were no significant differences in the bioactivity of the growth factor PDGF at different concentrations (0 ng/mL, 18 ng/mL, and 180 ng/mL) at day 0 and seven months later. In addition, the bioactivity of the growth factor PDGF prepared in above was measured under repeated freezing (−80° C.) and thawing (0° C.) mode. As shown in FIG. 2, repeated freezing-thawing did not reduce bioactivity of the growth factor PDGF. The bioactivity of the growth factor PDGF at different concentrations (18 ng/mL and 180 ng/mL) did not decrease after one, two or three freeze-thaw cycles. Based on the above results, the growth factor PDGF prepared can maintain its bioactivity for at least seven months under storage temperature of −80° C. and had considerable stability in repeated freeze-thaw cycles.

Example 4: Bioactivity Test at Room Temperature or Above

Since the bioactivity of a PDGF solution was very stable under storage temperature of −80° C. and was not susceptible to repeated freeze-thaw cycles, its stability above room temperature was examined. The PDGF prepared as above in Example 1 was dissolved in DMEM and diluted to 180 ng/mL, and incubated at 37° C. for 0, 2, 4, 6, 12, 24, 36, and 48 hours, respectively. The bioactivity of PDGF was measured with a commercially available Human PDGF FlowCytomix Simplex Kit (Invitrogen) and flow cytometry was used to measure bioactivity. The results in FIG. 3 showed that the PDGF was very unstable at 37° C.

In addition, the PDGF prepared was dissolved in DMEM and diluted to 180 ng/mL, then mixed with 9 mg/mL of collagen. After incubation at 37° C. for 6 hours, the bioactivity was measured, as shown in FIG. 4. The results showed that, at the same concentration (180 ng/mL), the growth factor without added collagen had higher bioactivity. Even if 9 mg/mL of collagen was added to the growth factor solutions at concentrations 900 ng/mL, 1800 ng/mL, and 9000 ng/mL, respectively (see Table 1), the bioactivity did not increase relatively with the growth factor concentration. The results indicated that the release of PDGF was controlled when combined with collagen and demonstrated a lower bioactivity than PDGF solution alone.

TABLE 1 PDGF concentration Collagen concentration Concentration (ng/ml) (mg/ml) Ratio  180 9 2 * 10⁻⁵:1  900 9 1 * 10⁻⁴:1 1800 9 2 * 10⁻⁴:1 9000 9 1 * 10⁻³:1

Example 5: Preparation of a Growth Factor Composition at Room Temperature

The native growth factor prepared in Example 1 was combined with collagen and then lyophilized 100 μL of solutions each containing 3 mg/mL of collagen and different concentrations of the growth factor (0, 30, 60, 90, 120, 150, 180, 360 or 900 ng/mL) were prepared. See Table 2. The collagen-growth factor solutions were frozen at −80° C. for 8 hours, and then lyophilized by a freeze dryer. The conditions of the freeze dryer are shown in Table 3.

TABLE 2 PDGF Concentration Collagen Concentration Concentration (ng/ml) (mg/ml) Ratio  30 3   1 * 10⁻⁵:1  60 3   2 * 10⁻⁵:1  90 3   3 * 10⁻⁵:1 120 3   4 * 10⁻⁴:1 150 3   5 * 10⁻⁵:1 180 3   6 * 10⁻⁵:1 360 3 1.2 * 10⁻⁴:1 900 3   3 * 10⁻⁴:1

TABLE 3 Temperature Time (° C. ) (min) 16  10 18  10 20 120 22 120

The results in FIG. 5 showed that the control group, PDGF solution, exhibited the highest bioactivity at 120 ng/mL (3.4×10⁵ RLU/sec). However, as the growth factor concentration increased, the bioactivity decreased relatively, showing the occurrence of inhibition. In the experimental group, the growth factor had a bioactivity of 3.1×10⁵ RLU/sec at a concentration of 30 ng/mL, and its bioactivity increased relatively as the concentration of the growth factor increased. Besides, the bioactivities of the growth factor at various concentrations lyophilized with collagen were higher than the bioactivities of its corresponding growth factor solution. The results indicate the bioactivity was preserved by lyophilized collagen.

Three forms of growth factor, aqueous solution, lyophilized powder, and lyophilized with collagen, were produced with 0, 60, and 180 ng/mL of PDGF and their bioactivities measured by luciferase assay were compared after incubation at room temperature for 0, 1, 2, 3, and 7 days, and even up to 6 months. The samples were used to treat 293-SL/PR cells for 30 min and their luciferase activity measured. The lyophilized powder group showed baseline luciferase activity, the PDGF solution showed initial luciferase activity before day 1, and the lyophilized with collagen group showed persistent luciferase activity throughout 6 months of examination (data not all shown). See FIG. 6. The PDGF in the aqueous solution group at 60 ng/mL and 180 ng/mL showed bioactivity at day 0. However, the bioactivity decreased rapidly thereafter. After one day of incubation, the bioactivity of the aqueous solution group was the same as the lyophilized powder group. Compared with the 60 ng/mL PDGF solution group, the bioactivity of the 60 ng/mL lyophilized with collagen combination group was higher, and even slightly increased after 1 day of incubation; the bioactivity was maintained for 6 months (data not shown). The same phenomenon was observed in the 180 ng/mL of PDGF lyophilized with collagen combination group.

The above results showed that the growth factor prepared by mixing with collagen followed by lyophilization exhibited higher and stable bioactivity at room temperature.

Example 6: Preparation of Native Growth Factors

Some growth factors were purchased from commercial resources. In some cases, the native human growth factor gene was purchased from Addgene Headquarters, USA or other resources. The expression vector of the growth factor gene was constructed and screened. It was then overexpressed in a yeast expression system or other suitable expression systems such as CHO cell system and insect system. The expressed growth factor protein was then harvested and purified. Once purified, the growth factor protein was aliquoted and stored at −80° C. to preserve its activity for use.

Example 7: Drying Step

The native growth factor prepared as above was frozen at −80° C. and then lyophilized. The lyophilization procedure involved removing ice from the growth factor by sublimation under vacuum condition or under very low pressure. For mixing with collagen, two procedures were taken: (1) Both collagen and growth factor in solutions were mixed initially and followed by a drying step to evaporate water gas under a low atmospheric pressure or a freeze-drying procedure using a lyophilizer; and (2) Collagen was dried initially and immersed in or sprayed with a growth factor solution, followed by a drying step as described above.

Example 8: Bioactivity Measurement by Cell Proliferation Performance

NIH3T3 cells were seeded at 1.2×10⁴ cells/cm² in a 48-well cultural plate. After cell attachment in DMEM-10% FBS for 24 hours, different concentrations as well as various growth factors in DMEM-1% FBS were cultured at 37° C. in an incubator with 5% CO₂. After being cultured for another 3 days, the cells were lysed with sterilized water and DNA was released by freeze-thaw cycles between −80° C. and room temperature. After transferring DNA samples to black fluorescence detection plate, 2 μg/ml of Hoechst 33258 in 1×TNE buffer was added to each well and the fluorescence intensity was detected under excitation at 365 nm and emission at 460 nm. The cell numbers were calculated from cell number standards, which were confirmed by the above DNA detection and cell counting.

Since bioactivities of growth factors in FIGS. 7 and 8 were measured by cell proliferation performance as described above, the efficacy of growth factor on cell proliferation corresponded well to its bioactivity throughout the assay period of 3 days. Various growth factors as indicated at either 100 ng/mL (FIG. 7) or 500 ng/mL (FIG. 8) were mixed with 10 mg/mL or 60 mg/mL of collagen solution or dropped on the indicated dried collagen, and this was followed with water evaporation by a speed vacuum system. There were 6 experimental groups and 6 result bars for each growth factor studied are shown in FIGS. 7 and 8: (1) freshly prepared growth factor solution, (2) growth factor pre-mixed with 10 mg/mL collagen before lyophilization and stored at −80° C. before use, (3) growth factor pre-mixed with 60 mg/mL collagen before lyophilization and stored at −80° C. before use, (4) growth factor added to dried collagen at 60 mg/mL, lyophilized and stored at −80° C. before use, (5) same as (3) but stored at room temperature for 1 week before use, (6) same as (4) but stored at room temperature for 1 week before use.

The results in FIGS. 7 and 8 demonstrated that bioactivities of growth factors, aFGF, bFGF, VEGF165, VEGF121, PDGF, and EGF, in aqueous solutions were indeed lower than the bioactivities of corresponding growth factor in combination with collagen. Although the bioactivities varied for different growth factors, higher amount of collagen preserved the bioactivities of growth factors. Compare the second bar with the 3^(rd) to 6^(th) bars in both FIGS. 7 and 8. The storage temperature of the dried mixture of growth factor and collagen showed no significant impact on the bioactivities of the growth factors. Compare the 3^(rd) and 4^(th) bars (−80° C. storage) with the corresponding 5^(th) and 6^(th) bars (room temperature storage) in both FIGS. 7 and 8. The results indicated that the bioactivity of a growth factor can be preserved at room temperature when combined with collagen and the mixture should be kept dried. There was no significant difference between the methods of drying growth factor and collagen mixture.

It was found that the bioactivities of growth factors after mixing with collagen in a dry state could be preserved for years, and similar bioactivity level was observed for at least 12 months. It was also found that gelatin or collagen derivatives, in replacement of collagen, showed the same effects on bioactivity preservation for various of growth factors. Since the bioactivity of growth factor can be preserved by mixing with collagen in a dry state, it is reasonable that the bioactivity of growth factor can be also preserved by combining with other materials such as other extracellular materials.

Example 9: Bioactivity of Growth Factors can be Stabilized by Other Matrix Molecules

Twenty μl of 15 mg/ml 1560 KDa hyaluronan, 10 mg/ml gelatin or 10 mg/ml albumin containing 100 or 500 ng/ml of growth factor (bFGF and EGF) were prepared respectively and added to 48-well culture plate. The culture plate was frozen for 4 h at −80° C. and lyophilized for 2 h. One plate was stored at 25° C. for 2 days, and the other was stored at −80° C.

NIH3T3 (1.2×10⁴ cell/cm²) were seeded to 48-well culture plates and incubated with DMEM-10% FBS until cells attached. This was followed by a medium change to DMEM—1% FBS with indicated concentrations and conditions of growth factors. At day 4, cells were lysed by the freeze-thawing method. Hoechst 33258 (Advancing Assay Technologies Bioquest) was prepared with TNE buffer (10 mM Tris-base, 1 mM EDTA, 200 mM NaCl, pH 7.4), and was added to the plates and allowed to stand at room temperature for 10 minutes. A fluorescence reading was taken with excitation at 365 nm and emission at 460 nm (MDI SpectraMax M2e). Although data may vary with the matrix molecule applied, the amount of matrix molecule, kind of growth factor, and the ratio of the growth factor to the matrix molecule in a composition, the results indicated that gelatin, hyaluronan, and albumin can preserve the bioactivity of various growth factors to certain extents. 

1. A method for preserving a bioactivity of a growth factor, comprising: providing a solution containing a concentration of a native growth factor and a concentration of a matrix molecule, wherein the concentration of the native growth factor and the concentration of the matrix molecule is at a ratio of 1×10⁻⁹ to 1:1; and performing a drying process to the solution, thereby obtaining a growth factor composition with the bioactivity of the growth factor preserved.
 2. The method of claim 1, wherein the drying process is a lyophilization process.
 3. The method of claim 1, wherein the matrix molecule is a collagen, a collagen derivative, a gelatin, a hyaluronan, or a combination thereof.
 4. The method of claim 1, wherein the concentration of the matrix molecule is 1 to 100 mg/ml, optionally, the concentration of the matrix molecule is 3 to 60 mg/ml.
 5. (canceled)
 6. The method of claim 1, wherein the concentration of the growth factor is 1 ng/mL to 1 μg/mL.
 7. The method of claim 1, wherein the ratio of growth factor to matrix molecule is 1.67×10⁻⁸ to 3.33×10⁻⁴:1.
 8. The method of claim 1, wherein the growth factor composition is stored at −80° C.˜37° C.
 9. The method of claim 1, wherein the matrix molecule is a collagen.
 10. The method of claim 1, wherein a bioactivity of the growth factor is preserved for at least 7 days at room temperature.
 11. The method of claim 1, wherein the native growth factor is selected from the group consisting of platelet-derived growth factor (PDGF), epidermal growth factor (EGF), keratinocyte growth factor (KGF), transforming growth factor (TGF-α, TGF-β), fibroblast growth factor (FGF), stem cell factor (SCF), insulin-like growth factors (IGF-I, IGF-II), nerve growth factor (NGF), bone morphogenetic protein (BMP), connective tissue growth factor (CTGF), vascular endothelial growth factor (VEGF), colony stimulating factor (CSF, M-CSF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, erythropoietin (EPO), endothelial cell monocytes active polypeptide (endothelial-monocyte activating polypeptide), epithelial neutrophil activating peptide, glial derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor (GMCSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), interleukin, serotonin, tumor necrosis factor (TNF), and von Willebrand factor.
 12. The method of claim 1, wherein the solution further includes a material selected from the group consisting of a cell attachment material, a tissue repair material, a cell induction material, an antibacterial material and a combination thereof.
 13. A growth factor composition prepared by a procedure including the method of claim 1, comprising: a concentration of a native growth factor; and a concentration of a matrix molecule; wherein the concentration of the native growth factor and the concentration of the matrix molecule is at a ratio of 1×10⁻⁹ to 1:1 and a bioactivity of the native growth factor is preserved.
 14. The growth factor composition of claim 13, wherein the matrix molecule is a collagen, a collagen derivative, a gelatin, a hyaluronan, or a combination thereof.
 15. (canceled)
 16. The growth factor composition of claim 13, wherein the concentration of the collagen is 3 mg/ml to 60 mg/ml.
 17. The growth factor composition of claim 13, wherein the growth factor is selected from the group consisting of platelet-derived growth factor (PDGF), epidermal growth factor (EGF), keratinocyte growth factor (KGF), transforming growth factor (TGF-α, TGF-β), fibroblast growth factor (FGF), stem cell factor (SCF), insulin-like growth factors (IGF-I, IGF-II), nerve growth factor (NGF), bone morphogenetic protein (BMP), connective tissue growth factor (CTGF), vascular endothelial growth factor (VEGF), colony stimulating factor (CSF, M-CSF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor, erythropoietin (EPO), endothelial cell monocytes active polypeptide (endothelial-monocyte activating polypeptide), epithelial neutrophil activating peptide, glial derived neurotrophic factor (GDNF), granulocyte colony-stimulating factor (GCSF), granulocyte macrophage colony-stimulating factor (GMCSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), interleukin, serotonin, tumor necrosis factor (TNF), and von Willebrand factor.
 18. The growth factor composition of claim 13, wherein the composition was further stored in −80° C.˜37° C.
 19. The growth factor composition of claim 13, wherein the bioactivity can be preserved for at least 7 days at room temperature.
 20. The growth factor composition of claim 13, wherein the composition further includes a material selected from the group consisting of a cell attachment material, a tissue repair material, a cell induction material, an antibacterial material and a combination thereof.
 21. The growth factor composition of claim 13, wherein the antibacterial material is an antibiotic, an antimicrobial protein, an antimicrobial peptide and a combination thereof.
 22. The growth factor composition of claim 13, wherein the cell attachment material is a saccharide, a peptide, a protein, a phospholipid, and a combination thereof; optionally, the saccharide material is a glycosaminoglycan material; optionally, the glycosaminoglycan material is selected from the group consisting of chondroitin, chondroitin sulfate, heparin, heparan sulfate, heparan sulfate proteoglycan, hyaluronan, and a combination thereof. 23-24. (canceled) 